Compositions of alkenyl aromatic resins and diorganopolysiloxanes



United States Patent 12 Claims. (Cl. 260-827) This application is a continuation of application Serial No. 406,578, filed January 27, 1954, now abandoned.

This invention concerns certain new thermoplastic compositions of matter comprising alkenyl aromatic resins and diorganopolysiloxane elastomers.

The new compositions are water resistant, possess excellent electrical properties even after exposure to moisture, are resistant to deterioration upon aging in the presence of air, light, heat, or oxygen, and can be molded to form articles having good mechanical properties such as impact strength and percent elongation. The new compositions can be molded by usual compression, injection molding or extrusion operations to form plastic articles suitable for a variety of purposes. The compositions are useful for making molded plastic articles having good electrical properties.

The new composi'ons are prepared by incorporating a minor amount of a non-liquid benzene-soluble diorganopolysiloxane containing in chemically combined form a plurality of siloxane units of the type R SiO wherein each R is selected from the group consisting of the methyl and phenyl radicals, and in which siloxane at least 90 percent of the total R groups are methyl radicals, with a major amount of thermoplastic alkenyl aromatic resin such as polystyrene, or a copolymer of a major proportion of styrene and a minor proportion of alpha-methylstyrene.

As the alkenyl aromatic resin starting material there may be employed a thermoplastic polymer of at least one mono-alkenyl aromatic compound of the benzene series. Homopolymers of monovinyl aromatic hydrocarbons, or nuclear halogenated derivatives thereof, such as styrene, ortho-, metaand para-vinyltoluene, vinylxylene, ar-ethylvinylbenzene, ar-chlorostyrene, or isopropylvinylbenzene, or copolymers of any two or more of such monovinyl aromatic compounds, or copolymers of a predominant proportion of at least one such monovinyl aromatic compound and from 1 to 35 percent by weight of an alphaalkyl-alkenyl aromatic hydrocarbon such as alpha-methylstyrene, para-methyl alpha-methylstyrene, or alpha-ethylstyrene, are preferred.

The diorganopolysiloxanes to be employed in accordance with the present invention are non-liquid benzenesoluble gummy to dough-like diorganopolysiloxanes containing in chemically combined form a plurality of siloxane units having the structural formula R SiO wherein each R is a member of the group consisting of the methyl and phenyl radicals, and in which siloxane at least 90 percent of the total R groups are methyl radicals. The polysiloxane may be one in which all of the siloxaneunits are (CI-l SiO, or the siloxane may be a coploymer of dimetbylsiloxane and a minor amount of any combination of the units C H (CH )SiO, or (C H SiO. The diorganopolysilorcane elastomers contain a plurality, e.g. from 2,700 to 10,000, or more, of the above-mentioned siloxane units. The diorganopolysiloxanes are unvulcanized polymers and are completely soluble in benzene. They may be prepared in known Ways such as by catalytic polymerization of suitable diorganosiloxanes employing a procedure similar to that described in United States Patent No. 2,541,137. The diorganopolysiloxanes may be used 3,239,579 Patented Mar. 8, 1966 ICC in admixture with, i.e. as a composition containing, a finely divided silica in amount corresponding to 50 percent by Weight or less of the composition. The aforementioned patent describes a number of unvulcanized diorganopolysiloxanes and mixtures of such polymers and finely divided silica which are suitable as starting materials for making the compositions of the invention. The term diorganopolysiloxane elastomer used herein refers to the unvulcanized benzene-soluble polymers and copolymers of diorganosiloxanes just mentioned and compositions of such polymers including up to 50 per-cent by weight of a finely divided silica.

The alkenyl aromatic resin and the diorganopolysiloxane elastomer starting materials are usually employed in proportions corresponding to from 50 to 98, preferably from to 98, percent by Weight of the alkenyl aromatic resin and from 50 to 2, preferably from 15 to 2, percent of the diorganopolysiloxane elastomer.

The compositions are usually prepared by heat-plastifying a blend, or dry mix, of the granular alkenyl aromatic resin and the diorganopolysiloxane elastomer in the desired proportions and mechanically working the heated mixture to form a homogeneous composition. Mixing or compounding the ingredients with one another may be carried out in a Banbury mixer, or on heated compounding rolls, in known ways. Usually, the addition of a small amount of a liquid plasticizer having a boiling point above 200 C. such as n-butylstearate, soybean oil, or a White mineral oil, in proportions corresponding to from 0.5 to 5 percent by weight of the composition, is of advantage as an aid to incorporating the heat-plastified ingredients with one another. The liquid plasticizer may be added to the heat-plastified ingredients while mechanically working the same at elevated temperatures, or it may be incorporated with the alkenyl aromatic resin during formation of the same, e.g. by dissolving the liquid plasticizer in the monomeric alkenyl aromatic compound and polymerizing the latter. Small amounts of organic peroxides having decomposition temperatures above C. such as benzoyl peroxide, di- (tertiary-butylpenphlthalate) tertiary butylpercaprylate, or tertiary-butylperbenzoate, may also advantageously be added to the heat-plastified mixture of ingredients, while mechanically working the same, in amount corresponding to from 0.01 to 0.5 percent by weight of the composition. It may be mentioned that a peroxy compound is advantageously added to the composition after the heatplastified alkenyl aromatic resin and the diorganopolysil-oxane elastomer have been mechanically worked in admixture with one another to produce a substantially uniform composition, then further working the heated mixture to uniformly mix the per-oxy compound with the composition. The addition of a per-oxy compound, e.g. tertiary-butylperbenzoate, to a diorganopolysiloxane elastomer and heating at elevated temperatures usually results in vulcanization or cross-linking of the silox'ane and may cause the formation of a non-uniform com-position by cross-linking of the siloxane elastomer when the peroxy compound is added prior to intimately incorporating the polymeric ingredients with one another.

In a preferred practice, the alkenyl aromatic resin is heat-plastified, e.g. by milling on heated compounding rolls, or by heating and kneading in a Banbury mixer. The diorganopolysiloxane elastomer is added in the desired proportion. The mixture is mechanically worked at temperatures between and 250 C. to incorporate the ingredients with one another and produce a homogeneous or substantially uniform composition. Usually, mechanical working of the mixture on heated rolls, or by kneading in a Banbury mixer, for a time of from 3 to 15 minutes is sufficient to result in the formation of a uniform composition, although mechanical working of cedure'the heat-plastifiedcomposition may be sheeted out, or fed to a plastics extrude-r and formed into thin bands, sheets, ribbons, or rods, then cooled and cut or ground to a granular form. Small amounts of dyes, pig-- ments, or other coloring agents may be incorporated with the composition, together With a liquid plasticizing, agent such as n-butyl-stearate, soybean oil, or a white mineral oil, as previously mentioned.

The following examples illustrate 'ways in which the principle of the invention has been applied but are not to be construed as limiting its scope.

EXAMPLE 1 A charge of 1440 grams of molding grade polystyrene containing one percent by weight of white mineral oil as lubricant was heat-plastified by kneading in a Banbury type laboratory mixer at a temperature of 162 C. Thirty grams of a batch of a diorganopolysiloxane elastomer, comprising Weight of a dough-like non-flowing benzene-soluble dimethylpolysiloxane and 35 parts of finely divided fume silica, i.e. silica prepared by burning silicon tetrachloride and condensing the vaporized SiO was added and mixed with the he-at-plastified polystyrene. Thereafter, 30 grams of butyl stearate was added and the resulting mixture kneaded for a period of 6 minutes, then removed from the mixer and allowed to cool to room temperature. molding. molded to form test bars of cross section. These test bars were used to determine the tensile strength, percent elongation and impact strength values for the composition. The procedure for determining tensile strength and percent elongation was similar to that described in ASTM D63 8-44T, and the procedure followed in measuring impact strength was similar to that described in ASTM alternating current having a frequency of 10 second the dielectric constant and the percent power factor in accordance with procedure described in ASTM D150-44T. The dielectric constant and percent power factor were determined on test pieces after conditioning in air at 25 C. and 50 percent relative humidity for 24 hours, and on test pieces after immersion in water at 25 C. for 24, 48 and 168 hours, respectively. The co-m position had the properties given in Table I.

cycles per an intimate mixture of 100 parts by It was crushed to a granular form suitable for Portions of the composition were injection /s x /2 inch rectangular D256-43T. Other molded test pieces were used to determine under the action of an Table 1 Test N 0 Mechanical Properties 1 Tensile Strength, lbs/sq. in 5, 140 2 Elongation, percent 14 3 Notched Impact Strength, tt.-lbs 0. 91

Electrical Properties Frequency, Dielectric Percent Conditioning cycles/sec. Constant Power Factor 24 Hrs. in air 10 2. 52 0. 01 24 Hrs. in H2O 10 2. 53 0.05 48 Hrs. in H2O 10 2. 54 0.07 168 Hrs. in H O 10 2. 54 0.08 v

F; and the 4 i EXAMPLE 2 A charge, of 288 grams of polystyrenewas heat-plastified by milling the same on a pair of 3-inch diameter by 8 inches long internally steam heated laboratory rolls. 240 F: and the other. roll was heated of 300 at .a temperature oxane described in Example -1 was added. The resultirrg mixture was milled on the heated rolls for a period. of 6 minutes, then removed and-allowed to cool to room temperature.- It was crushed to a granular form suit? able for molding. Molded test "bars were prepared from the composition and tested as described in Examample 1. The .composition 'had the properties:

EXAMPLE 3 A charge of '147 gramstof molding gradepolystyrene containing one percent by weight of white :mineral vtoil as lubricant was heatplastified by milling the .same on the heated laboratory rolls described in Example 2..

Thereafter, 147 grams of the. batch of the diorganopolysiloxane described ,in Example on the rolls heated at. temperatures of 240 and: 300 F.', respectively, for 6 minutes, thenzremoved and cooled to room temperature. form. Molded test pieces'of the as described tin-Example l.

composition were tested The composition hadthe properties:

Tensile. strength,:lbs./sq. in. .480 Elongation, percent 2.3 Notched impact strength, ft.-lb. 0.74 Dielectric constant (initial) 2.67 a Power factor (initial), percent- 0.14 Dielectric constant (after 120 hrs. in H O) 2.91'- Power factor (after. 120 hrs. in H O), percent 0.22 l

EXAMPLE 4 of molding the'following table was heateplastifie'd by millirrghthe same on the laboratory rolls described in Example 2,

while heating one of the rolls at a temperature of 280 other roll at a temperature of 320 F5 After heat-plastifyling the polystyrene .on the rolls, a portion of a batch prising an intimate mixture of parts by weight of a dough-like non-flowingbenzene-soluble dimethylpolysiloxane and 45 parts of finely divided trimethylchlorosiloxane-treated fume silica, was addedtogether' with butylstearate, in proportions as stated in'the table. The.

resulting mixture was compoundedon the .heated rolls for 6 minutes, then removed and cooled to room temperature.

composition were tested by procedure similar to those described in Example 1. Table II identifies eaclrcomof the ingredients used The percent power factor hours.

- One of the rolls washeated ata temperature of- F. After heat-plastifyingqthe polystyrene on the rolls, 12 grams of the batch ofxthe:diorganopolysil- Land 6'grams of-butylstearate was added. The resulting mixturewas milled.

It was, crushed to, :a granular .of a diorganopolysiloxane elastorner, com

The composition was crushedtoa granularv form' suitable for molding. Molded testpieces ofhthe Table II Starting Materials Product No. Poly- Silicone Butyl Tensile Notched Elonga- Power styrene, Rubber, Stearate, Strength, Impact tion, Factor, percent percent percent lbs/sq. in. Slgelilgth, percent percent EXAMPLE 5 miXer. A charge of 7.6 pounds of a concentrate, previ- In each of a series of experiments, 300 grams of a composition comprising polystyrene, a diorganopolysiloxanes elastorner and n-butyl stearate in proportions as stated in the following table was prepared by procedure similar to that described in Example 2. The polystyrene employed in the experiments was in the form of molding granules and contained one percent by weight of white mineral oil as lubricant. The diorganopolysiloxane elastomer was .an intimate mixture of 100 parts by weight of a benzene-soluble gummy copolymer of 95 mole percent dimethylsiloxane and 5 mole percent phenylmethylsiloxane, and 30 parts of Santocel C (a finely divided silica gel substantially free from sodium sulfate). After milling the ingredients with one another on the heated laboratory rolls for a time of approximately six minutes, the composition was removed and allowed to cool to room temperature. Molded test bars of the composition were tested by procedure similar to those described in Example 1. Table III identifies each composition by giving the proportion of ingredients in percent by weight from which it was prepared. The table also gives the properties for each composition. The percent power factor was determined on molded test pieces after conditioning in air at 25 C. and 50 percent relative humidity for 24 hours.

ously prepared by compounding equal parts by weight of the batch of polystyrene and a diorganopolysiloxane elastomer composed of an intimate mixture of 100 parts by weight of a non-flowing benzene-soluble dough-like dimethylpolysiloxane and parts by weight of fume silica with one another at temperatures between 350 and 370 F. for a period of approximately 8 minutes, was added to the heat-plastified polystyrene in the Banbury mixer. The mixture was kneaded at temperatures between 150 and 190 C. for a period of 11 minutes while adding 0.1 pound of color pigment and 1.9 pounds of n-butyl stearate, after which the mixture was kneaded for 5 minutes longer, than fed to a plastics extruder and extruded, cooled and cut to a granular form suitable for molding. A portion of the composition was injection molded to form test bars /8 x /2 inch cross section by 4 inches long. The test bars were used to determine tensile strength, percent elongation and impact strength values for the composition by procedures as described in Example 1. Other molded test pieces were used to determine the heat distortion temperature by a procedure of Heirholzer and Boyer ASTM Bulletin No. 134 of May 1945, and to determine under the action of an alternating current having a frequency of 10 cycles per second the dielectric con stant and the percent power factor in accordance with Table III Starting Materials Product Run No. Poly- Silicone Butyl Tensile Notched Elonga- Power styrene, Rubber, Stearate, Strength, Impact tron, Factor, percent percent percent lbs/sq. in. Streililgth, percent percent EXAMPLE 6 procedures described in ASTM D150-44T. The dielectric A charge of 285 grams of polystyrene having a viscosity characteristic (10 percent by weight solution in toluene) of centipoises at 25 C. was heat-plastified by milling the same on the laboratory rolls described in Example 2, heated at 240 F. and 300 F., respectively. Fifteen grams of a benzene-soluble gummy polyorganosiloxane consisting of a copolymer of mole percent dimethylsiloxane and 5 mole percent phenylmethylsiloxane was added thereto. The mixture was compounded on the heated rolls for a period of six minutes, then removed and allowed to cool to room temperature. Molded test bars of the composition were tested as described in Example 1. The composition had the properties:

Tensile strength, lbs/sq. in. 5030 Elongation, percent 9.8 Notched impact strength, ft.-lb 0.54 Dielectric constant (initial) 2.36 Power factor (initial), percent 0.03 Power factor (after hrs. in H O), percent 0.05

EXAMPLE 7 A charge of 89.2 pounds of a batch of molding grade polystyrene containing one percent by weight of white mineral oil was heat-plastified and kneaded in a Banbury constant and percent power factor were determined on test pieces after conditioning in air of 50 percent relative humidity at 25 C. for 24 hours and on test pieces after immersion in water at 25 C. for a period of time as indicated in the following table. The composition had the properties given in Table IV.

Table IV Test No Mechanical Properties Tensile Strength lbs/sq. in 4 225 Notched Impact 'Strength, ft.-lbs ii. 78 Elongation, percent 21. 6 Heat Distortion Temp, C 74 Electrical Properties Frequency, Immersion Dielectric Percent cycles/sec. Time, Hrs. Constant Power Factor 7 EXAMPLE 8 A charge of 288 grams of polyvinyltoluene, prepared by polymerizing a mixture of approximately 65 percent by weight of meta-vinyltoluene and 35 percent para-vinyltoluene in bulk, was heat-plastified by milling the same on the laboratary rolls heated at temperatures'of 240 F.

and 320 F, respectively, described in Example 2. Twelve grams of a batch of a diorganopolysiloxane elastomer composed ofan intimate mixture of 100 parts by weight of a nonflowing benzene-soluble dough-like dimethylpolysiloxane and 35 parts of fume silica, was added. The

mixture was compounded on the heated rolls for 6 minutes, then vremoved and allowed to cool.

Example 1. Other molded test pieces were used to determine the dielectric constant and percent power factor under theaction of an alternating current having a frequency of 10 cycles per second by procedures similar to those described in ASTM D150-44T. The dielectric constant and power factor were determined on 'test pieces after conditioning in air of 50 percent relative humidity at C. for 24 hours and after immersion in water at 25 C. for 120 hours. The composition had the properties:

Tensile strength, lbs/sq. in. 4250 Elongation, percent 16.4 Notched impact strength, ft.-lb. 0.98 Dielectric constant (initial) 2.49 Power factor (initial), percent 0.06 Dielectric constant (after 120 hrs. in H O) 2.54 Power factor (after 120 hrs. in H O), percent 0.10

EXAMPLE 9 A charge of 288 grams of copolymer of 85 percent styrene and 15. percent alpha-methylstyrene was heatplastified by milling on the laboratory rolls heated at 240 F. and 320 F., respectively, described in Example 2. Twelve grams of the batch of the diorganopolysiloxane elastomer described in ExampleS were added and the.

mixture compounded on the heated rolls for 6 minutes, then removed and allowed to cool. of the composition were tested by procedures as described in Example 1. The composition had the properties:

Molded test pieces of the composition were tested as described in Molded test pieces Tensile strength, lbs/sq. in 4380 Elongation, percent .14.6 Notched impact strength, ft.-lb. 0.56 Dielectric constant (initial) 2.51 Power factor (initial), percent 0.03 Dielectric constant'(after 120 hrs. in H O) 2.55 Power factor (after 120 hrs. in H O), percent 0.04

EXAMPLE 10 A charge of 288 grams of poly-ar-chlorostyrene, prepared by polymerizing a mixture of approximately percent by weight of para-chlorostyrene and 50 percent ortho-chlorostyrene in bulk, was heat-plastified by milling on the laboratory rolls heated at a temperature of 280 F. and 398 F., respectively, described inExample 2. Twelve grams of the batch of the diorganosiloxane elastomerdescribed in Example 8 was added. The mixture was compounded on the heated rolls for 6 minutes,

then removed and allowed to cool. Molded test pieces of the composition were tested by procedures as described in Example 1. The composition had :the

properties:

Tensile strength, lbs./ sq. in 4640 Elongation, percent 13.8 Notched impact strength, ft.-lb 0.47 Dielectric constant (initial) 2.67 Power factor (initial), percent 0.07 Dielectric constant (after 120 hrs. in H 0) 2.69 1 Power factor (after 120 hrs. in H O), percent 0.13

We claim:

1. A thermoplastic composition consisting essentially of an intimate mixture ;of from 50 to: 98 percent; by 1 weight of at least one alkenyl aromatic resin selected from the group consisting of (a). homopolymers and copolymers of said monovinyl aromatic compounds with each other and (b) copolymers of fromto 99 percent by weight of at least one such monovinyl aromatic com:

pound of the. benzene series and from 35 to 1 percent of an alkenyl aromatic hydrocarbon selected from the group consisting of alpha-methylstyrene, ,para-methyl-alphamethylstyrene and alpha-ethylstyrene, and from '50 to 2.

percent by weight, of a non-liquid benzene-soluble diorganopolysiloxane. elastomer' in which the siloxane' units are of the type R SiO; wherein each R is selected from the group consisting of the methyl and phenyl radicalsat least percent of the total R groups in the siloxane being methyl radicals, and said elastomer containing in chemie least one alkenyl aromatic resin selected from the group consisting of (a) homopolymers ofmonovin'yl aromatic compounds selected from the group consisting of mono-,

vinyl aromatic hydrocarbons of the benzene series and, nuclear halogenated derivatives thereof, and 'copolymersof said monovinyl aromatic'co-mpounds with'each other, and (b) copolymers of from 65 to 99 percentby weight of at least one such monovinyl aromatic compound of the benzene series and from 35 to, 1 percentof an alkenyl aromatic hydrocarbon which is a member of the group consisting of alpha-methylstyrene, ,para-methyl-alpha methylstyrene and alpha-ethylstyrene, and from' 15 to 2.

percent by weight of a non-liquid benzene-soluble diorgano-polysiloxane elastomer in whichthe siloxane-units are of the type R SiO, wherein each R is selectedfrom the group consisting of the methyl and phenyl radicals, at

least 90"percent of the ,total-R groups in thesiloxanefl being methyl radicals and, said elastomer containing in chemically combinedform between 2,700 and 10,000 of the siloxane units.

6. Acomposition as .claimedinclaim 5,= wherein the alkenyl aromatic resinis a copolymer of at least 65 percent by weight of styrene and a lesser amount of alpha-.

methylstyrene.

7. A composition as claimedin claim 5,iwhrein the alkenyl aromatic resin is a homopolymer'of'vinyltoluene and the diorganopolysiloxane,elastomer is dimethylpolysiloxane.

8. A composition asclaimedinclaim 5,;whereinthe alkenyl aromati-c,..resin :isv a .homoplymer. of anchlorostyrene, and the diorganopolysiloxane elastomeris dimethylpolysiloxane. V

9. A composition as claimedin claim 5,;wherein the alkenyl' aromatic resin:is polystyrene and the: diorgano! polysiloxane elastomer is fa coplymer of at least 90 mole percent of dirne-thylsiloxane and a lesser mole percentof phenylmethylsiloxane, I V

10. "A method of makinga thermoplastic composition consisting essentially of an alkenyl aromatic resin and a diorganopolysiloxane elastomer, which method consists.

in heat-plastifying. andv mechanically workingin-admixe ture with one another at a temperature between and 250 C., (1) from 50 to 98 parts by'weight of at least one thermoplastic alkenyl aromatic resin selectedfrom the group consisting of (a) homopolymers ofmonovinyl;

aromatic compounds selected from the group consisting of 'monovinyl aromatic hydrocarbons of the benzene series and nuclear halogenated derivatives thereof, and copolymers of said monovinyl aromatic compounds with each other, and (b) copolymers of from 65 to 99 percent by weight of at least one such monovinyl aromatic compound selected from the group consisting of monovinyl aromatic hydrocarbons of the benzene series, and nuclear halogenated derivatives thereof, and from 35 t 1 percent of an alkenyl aromatic hydrocarbon which is a member of the group consisting of alpha-methyl styrene, para-methyl-alph'a-methylstyrene and alpha-ethylstyrene, and (2) from 50 to 2 parts by weight of a non-liquid benzene-soluble diorganopolysiloxane elastomer in which the siloxane units are of the type R2810, wherein each R is selected from the group consisting of the methyl and phenyl radicals, at least 90 percent of the total R groups in the siloxane being methyl radicals, and said elastomer containing in chemically combined form a plurality of the siloxane units.

11. A thermoplastic composition consisting essentially of an intimate mixture of from 50 to 98 percent by weight of polystyrene and from 50 to 2 percent by weight of a non-liquid benzene-soluble diorganopolysiloxane elastomer in which the siloxane units are of the type R SiO, wherein each R is selected from the group consisting of the methyl and phenyl radicals at least 90 percent of the References Cited by the Examiner UNITED STATES PATENTS 2,258,218 10/1941 Rochow 260827 2,541,137 2/1951 Warrick 26037 2,635,060 4/ 1953 Cheronis et a1. 260-827 2,698,314 12/1954 Rust 260827 2,792,309 5/ 1957 Teichrnann 260-827 2,888,424 5/1959 Precopio et al. 260-827 3,020,597 2/1962 Smith-Johannsen 2602.5

OTHER REFERENCES Boundy et al.: Styrene, published by Reinbold Pub. Corp., New York (1952), pages 1188-1189.

MURRAY TILLMAN, Primary Examiner.

LEON I. BERCOVITZ, Examiner. 

1. A THERMOPLASTIC COMPOSITION CONSISTING ESSENTIALLY OF AN INTIMATE MIXTURE OF FROM 50 TO 9898 PERCENT BY WEIGHT OF AT LEAST ONE ALKENYL AROMATIC RESIN SELECTED FROM THE GROUP CONSISTING OF (A) HOMOPOLYMERS AND COPOLYMERS OF SAID MONOVINYL AROMATIC COMPOUNDS WITH EACH OTHER AND (B) COPOLYMERS OF FROM 65 TO 99 PERCENT BY WEIGHT OF AT LEAST ONE SUCH MONOVINYL AROMATIC COMPOUND OF THE BENZENE SERIES AND FROM 35 TO 1 PERCENT OF AN ALKENYL AROMATIC HYDROCARBON SELECTED FROM THE GROUP CONSISTING OF ALPHA-METHYLSTYRENE, PARA-METHYL-ALPHAMETHYLSTYRENE AND ALPHA-ETHYLSTYRENE, AND FROM 50 TO 2 PERCENT BY WEIGHT OF A NON-LIQUID BENZENE-SOLUBLE DIORGANOPOLYSILOXANE ELASTOMER IN WHICH THE SLOXANE UNITS ARE OF THE TYPE R2SIO, WHEREIN EACH R IS SELECTED FROM THE GROUP CONSISTING OF THE METHYL AND PHENYL RADICALS AT LEAST 90 PERCENT OF THE TOTAL R GROUPS IN THE SILOXANE BEING METHYL RADICALS, AND SAID ELASTOMER CONTAINING IN CHEMICALLY COMBINED FROM A PLURALITY OF THE SILOXANE UNITS. 